Two step phosphor deposition to make a matrix array

ABSTRACT

A method of fabricating closely spaced pcLEDs ( 100 ) arranged in a matrix array ( 200 ) of perpendicular rows and columns comprises an initial phosphor deposition step in which phosphor ( 803, 905 ) is deposited at alternating locations (pixels) in the matrix array in a checkerboard pattern, so that the locations ( 504 ) in the array at which phosphor ( 803, 905 ) is deposited are not adjacent to each other. In a subsequent phosphor deposition step phosphor is deposited at the alternating locations at which phosphor was not deposited in the first deposition step. In between the two phosphor deposition steps, reflective or scattering structures ( 606 ) may be fabricated on sidewalls of the phosphor pixels to optically isolate pcLEDs in the resulting array from each other

FIELD OF THE INVENTION

The invention relates generally to phosphor-converted light emittingdiodes.

BACKGROUND OF THE INVENTION

Semiconductor light emitting diodes and laser diodes (collectivelyreferred to herein as “LEDs”) are among the most efficient light sourcescurrently available. The emission spectrum of an LED typically exhibitsa single narrow peak at a wavelength determined by the structure of thedevice and by the composition of the semiconductor materials from whichit is constructed. By suitable choice of device structure and materialsystem, LEDs may be designed to operate at ultraviolet, visible, orinfrared wavelengths.

LEDs may be combined with one or more wavelength converting materials(generally referred to herein as “phosphors”) that absorb light emittedby the LED and in response emit light of a longer wavelength. For suchphosphor-converted LEDs (“pcLEDs”), the fraction of the light emitted bythe LED that is absorbed by the phosphors depends on the amount ofphosphor material in the optical path of the light emitted by the LED,for example on the concentration of phosphor material in a phosphorlayer disposed on or around the LED and the thickness of the layer.

Phosphor-converted LEDs may be designed so that all of the light emittedby the LED is absorbed by one or more phosphors, in which case theemission from the pcLED is entirely from the phosphors. In such casesthe phosphor may be selected, for example, to emit light in a narrowspectral region that is not efficiently generated directly by an LED.

Alternatively, pcLEDs may be designed so that only a portion of thelight emitted by the LED is absorbed by the phosphors, in which case theemission from the pcLED is a mixture of light emitted by the LED andlight emitted by the phosphors. By suitable choice of LED, phosphors,and phosphor composition, such a pcLED may be designed to emit, forexample, white light having a desired color temperature and desiredcolor-rendering properties.

WO 2018/122520 A1 discloses a process for producing optoelectronicdevices including a matrix array of light emitting diodes and aplurality of photoluminescent pads that are located facing at least someof the light emitting diodes. WO 95/30236 A1 discloses a process formaking a pixelized phosphor structure by creating a plurality ofopenings in a substrate and depositing a phosphor into the openings. US2017/200765 A1 discloses a display device with a distributed Braggreflector structure between phosphor portions.

SUMMARY OF THE INVENTION

This specification discloses methods for fabricating closely spacedpcLEDs arranged in a matrix array of perpendicular rows and columns. Thephosphor may be deposited directly on the array of LEDs. Alternativelythe phosphor may be deposited on a carrier substrate in a matrix arraycorresponding to the array of LEDs and later transferred to the LEDs.

In either case in an initial phosphor deposition step phosphor isdeposited at alternating locations (pixels) in the matrix array in acheckerboard pattern, so that the locations in the array at whichphosphor is deposited are not adjacent to each other. Phosphor isdeposited at half, or about half, of the locations in the array in thisfirst step. In a subsequent phosphor deposition step phosphor isdeposited at the alternating locations at which phosphor was notdeposited in the first deposition step. In between the two phosphordeposition steps, reflective structures may be fabricated on side wallsof the phosphor pixels to optically isolate pcLEDs in the resultingarray from each other.

An advantage of this method is that there are typically no high aspectratio structures in the matrix array when the reflective structures aredeposited, which facilitates their deposition. Another advantage is thatthe spacing between the pixels is equal to the reflector thickness,which may be very thin. The reflector thickness may be, for example,less than or equal to about 10 microns, less than or equal to about 5microns, less than or equal to about 3 microns, or less than or equal toabout 0.2 microns.

Phosphor-converted LEDs fabricated by the methods disclosed herein maybe employed for example in microLED arrays used in displays, in LEDarrays used for illumination in automobiles (for example, inheadlights), and in flash light sources for cameras.

Other embodiments, features and advantages of the present invention willbecome more apparent to those skilled in the art when taken withreference to the following more detailed description of the invention inconjunction with the accompanying drawings that are first brieflydescribed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-sectional view of an example pcLED.

FIGS. 2A and 2B show, respectively, cross-sectional and top schematicviews of an array of pcLEDs.

FIG. 3A shows a schematic top view an electronics board on which anarray of pcLEDs may be mounted, and FIG. 3B similarly shows an array ofpcLEDs mounted on the electronic board of FIG. 3A.

FIG. 4A shows a schematic cross sectional view of an array of pcLEDsarranged with respect to waveguides and a projection lens.

FIG. 4B shows an arrangement similar to that of FIG. 4A, without thewaveguides.

FIG. 5 shows a schematic top view of an example checkerboard patternedstructure that may be employed in phosphor deposition methods describedherein.

FIGS. 6A-6I illustrate intermediate stages in the fabrication of a pcLEDarray by one variation of the phosphor deposition methods describedherein.

FIGS. 7A-7D illustrate intermediate stages in the fabrication of a pcLEDarray by another variation of the phosphor deposition methods describedherein.

FIGS. 8A-8B illustrate intermediate stages in the fabrication of a pcLEDarray by another variation of the phosphor deposition methods describedherein.

FIGS. 9A-9E illustrate intermediate stages in the fabrication of a pcLEDarray by another variation of the phosphor deposition methods describedherein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description should be read with reference to thedrawings, in which identical reference numbers refer to like elementsthroughout the different figures. The drawings, which are notnecessarily to scale, depict selective embodiments and are not intendedto limit the scope of the invention. The detailed descriptionillustrates by way of example, not by way of limitation, the principlesof the invention.

FIG. 1 shows an example of an individual pcLED 100 comprising asemiconductor diode structure 102 disposed on a substrate 104, togetherconsidered herein an “LED”, and a phosphor layer 106 disposed on theLED. Semiconductor diode structure 102 typically comprises an activeregion disposed between n-type and p-type layers. Application of asuitable forward bias across the diode structure results in emission oflight from the active region. The wavelength of the emitted light isdetermined by the composition and structure of the active region.

The LED may be, for example, a III-Nitride LED that emits blue, violet,or ultraviolet light. LEDs formed from any other suitable materialsystem and that emit any other suitable wavelength of light may also beused. Other suitable material systems may include, for example,III-Phosphide materials, III-Arsenide materials, and II-VI materials.

Any suitable phosphor materials may be used, depending on the desiredoptical output from the pcLED.

FIGS. 2A-2B show, respectively, cross-sectional and top views of anarray 200 of pcLEDs 100 including phosphor pixels 106 disposed on asubstrate 202. Such an array may include any suitable number of pcLEDsarranged in any suitable manner. In the illustrated example the array isdepicted as formed monolithically on a shared substrate, butalternatively an array of pcLEDs may be formed from separate individualpcLEDs. Substrate 202 may optionally comprise CMOS circuitry for drivingthe LED, and may be formed from any suitable materials.

As shown in FIGS. 3A-3B, a pcLED array 200 may be mounted on anelectronics board 300 comprising a power and control module 302, asensor module 304, and an LED attach region 306. Power and controlmodule 302 may receive power and control signals from external sourcesand signals from sensor module 304, based on which power and controlmodule 302 controls operation of the LEDs. Sensor module 304 may receivesignals from any suitable sensors, for example from temperature or lightsensors. Alternatively, pcLED array 200 may be mounted on a separateboard (not shown) from the power and control module and the sensormodule.

Individual pcLEDs may optionally incorporate or be arranged incombination with a lens or other optical element located adjacent to ordisposed on the phosphor layer. Such an optical element, not shown inthe figures, may be referred to as a “primary optical element”. Inaddition, as shown in FIGS. 4A-4B a pcLED array 200 (for example,mounted on an electronics board 300) may be arranged in combination withsecondary optical elements such as waveguides, lenses, or both for usein an intended application. In FIG. 4A, light emitted by pcLEDs 100 iscollected by waveguides 402 and directed to projection lens 404.Projection lens 404 may be a Fresnel lens, for example. This arrangementmay be suitable for use, for example, in automobile headlights. In FIG.4B, light emitted by pcLEDs 100 is collected directly by projection lens404 without use of intervening waveguides. This arrangement mayparticularly be suitable when pcLEDs can be spaced sufficiently close toeach other, and may also be used in automobile headlights as well as incamera flash applications. A microLED display application may usesimilar optical arrangements to those depicted in FIGS. 4A-4B, forexample. Generally, any suitable arrangement of optical elements may beused in combination with the pcLEDs described herein, depending on thedesired application.

For many uses of pcLED arrays, it is desirable to compartmentalize thelight emitted from the individual pcLEDs in the array. That is, it isadvantageous to be able to operate an individual pcLED in the array as alight source while adjacent pcLEDs in the array remain dark. This allowsfor better control of displays or of illumination.

It is also advantageous in many applications to place the pcLEDs in thearray close together. For example, a preferred configuration inmicroLEDs is to have minimal spacing between the individual LEDs.Closely spacing the pcLEDs in an array used as a camera flash lightsource or in an automobile headlight may simplify the requirements onany secondary optics and improve the illumination provided by the array.

However, if pcLEDs in an array are placed close together, optical crosstalk between adjacent pcLEDs may occur. That is, light emitted by apcLED may scatter into or otherwise couple into an adjacent pcLED andappear to originate from that other pcLED, preventing the desiredcompartmentalization of light.

The possibility of optical crosstalk between pixels in an arrayprohibits the use of a single shared phosphor layer on top an array ofLEDs. Instead, patterned phosphor deposition providing a discrete pixelof phosphor on each light emitting element is needed, in combinationwith reflecting sidewalls on the phosphor pixels.

If the spacing between the LEDs in the array is small, for instancesmaller than 10 or 20 microns, it is difficult to form reflecting sidewalls on the phosphor pixels with wet chemical or physical depositionmethods due to the high aspect ratios of the channels to be filled orcoated. The most common scattering layer used as a side coat for LEDscomprises TiO2 scattering particles embedded in silicone. Another optionis a reflective metal layer, such as for instance aluminum or silver.Yet another option is a multilayer Distributed Bragg Reflector (DBR)structure formed from a stack of alternating layers of high and lowrefractive index material, which can provide very high reflectancedepending on design. To ensure uniform coating of such reflective layersor structures on the side walls of the phosphor pixels, the side wallsshould be accessible. If the aspect ratio of the gap between adjacentphosphor pixels is high, inhomogeneities in the reflective coatingthickness can be expected leading to non-uniform, non-optimal reflectingproperties.

This specification discloses a method of coating the side walls ofphosphor pixels that may be employed to produce a pcLED array with veryclose spacing of adjacent pcLEDs. As summarized above, in a firstphosphor deposition step only half (or about half) of the phosphorpixels are deposited, in a checkerboard pattern. For example, for amatrix array having an even number of pixels half of the phosphor pixelsmay be deposited in the first phosphor deposition step. For a matrixarray having an odd number of pixels half plus or minus 1 of thephosphor pixels may be deposited in the first phosphor deposition step.After the first phosphor deposition step (and removal of any patternedstructures or molds used in the first deposition step) the reflectingside coats are deposited. At this stage in the method no high aspectratio structures are present in the system to interfere with depositionof the reflecting side coats. In a following step the remaining phosphorpixels are deposited, leading to a pixelated matrix array of phosphorpixels each with reflecting side coats.

FIG. 5 shows a top view of an example 7×7 checkerboard pattern structure502 that may be used in this method. As further described below,structure 502 may be formed, for example, from a photoresist or as anoptionally reusable mold. Similar larger or smaller M×N structures maybe employed, in which M and N may be equal or may be different.Structure 502 comprises rectangular (e.g., square) openings 504alternating with rectangular (e.g., square) features of the structure toform the checkerboard pattern. These rectangular features of structure502 may be blocks of photoresist or portions of a mold, for example.Structure 502 further comprises thin rectangular openings 506 arrangedaround the edge of the checkerboard pattern adjacent to outer ones ofthe rectangular features in the structure.

As further described below, openings 504 are used to form phosphorpixels in the first phosphor deposition step. The function of openings506 is to provide, after the first phosphor deposition step, a surfaceonto which a mirror structure can be deposited. Otherwise the outerpixels formed during the second phosphor deposition step described belowwould lack an outer mirror structure. Phosphor deposited in openings 506is not used for light generation.

As an example, square openings 504 in structure 502 may be 200 micronsin width, and thin rectangular openings 506 may be 200 microns in lengthand 50 microns in width. The rectangular features in the checkerboardpattern of structure 502 are wider and longer than openings 504 by twicethe width of the reflective side coatings to be deposited on thepixelated phosphor array, in this example about two times 10 microns.The resulting pixel size and spacing may be suitable for a flash module,for example.

Smaller sizes may easily be created, for example 32×32 micron pixelswith 8 micron streets (pixel spacing, reflector width), 35×35 micronpixels with 5 micron streets, and 37×37 micron pixels with 3 micronstreets. Larger pixel sizes may be used as well. Any other suitabledimensions may be used.

FIGS. 6A-6I show a partial cross-sectional view of structure 502 takenalong cut line 503 shown in FIG. 5. Referring now to these figures, inone variation of this method checkerboard pattern 502 is formed fromphotoresist deposited on a carrier 602 (FIG. 6A). Any suitablephotoresist may be used, and the photoresist may be patterned using anysuitable conventional methods. Carrier 602 may be for example a glasssheet, or any other suitable material.

Subsequently, as shown in FIG. 6B, openings 504 in structure 502 arefilled with phosphor material to form phosphor pixels 604. Thinrectangular openings 506 in structure 502 are also filled with phosphormaterial at this step. The phosphor material may comprise, for example,any suitable phosphor particles dispersed in any suitable matrixmaterial. Suitable matrix materials may include, for example, silicones,sol gels, and low melting point glasses. The phosphor pixels may bedeposited by any suitable method, for instance by blade coating or byspray coating. Excess phosphor material may be removed from the top ofstructure 502 by, for example, rinsing or wiping or a combination of thetwo. Phosphor pixels 604 may then be cured or partially cured to such anextent that the photoresist forming structure 502 may be strippedwithout affecting the phosphor layer.

Subsequently, as shown in FIG. 6C, the photoresist forming structure 502is stripped from carrier 602, leaving phosphor pixels 604 with theirside walls exposed. The photoresist may be stripped with a solvent or bydry etching, for example, or by any other suitable method.

Optionally, after stripping of the photoresist the phosphor matrix canbe cured further. Also optionally, to arrest metal migration or toimprove adhesion of a reflecting layer on the phosphor pixels,intermediate layers may be deposited on the phosphor pixels or thephosphor pixels may be treated with a plasma or exposed to UV/Ozone.Subsequently, as shown in FIG. 6D, a reflecting layer 606 may bedeposited on the top and the side walls of phosphor pixels 604.Advantageously, at this stage the side walls of pixels 604 are easilyaccessed because the neighboring phosphor pixels have not yet beendeposited. Reflecting layer 606 may be or comprise, for example, a lightscattering material such as TiO2 particles embedded in silicone, one ormore reflective metal layers, or one or more DBR structures. Reflectivemetal layers may be deposited by vapor deposition or sputtering, forexample. DBR structures may be deposited by atomic layer deposition, forexample.

Reflective layer 606 may have a thickness on side walls of phosphorpixels 604 of, for example less than or equal to about 0.2 microns, lessthan or equal to about 3 microns, less than or equal to about 5 microns,less than or equal to about 10 microns, or less than or equal to about20 microns. An aluminum mirror reflective structure may have a thicknessless than or equal to about 0.2 microns, for example. A DBR structuremay have a thickness of less than or equal to about 3 microns, forexample. In the final phosphor array structure, the thickness of thesereflector sidewalls is also the spacing between phosphor pixels.

Subsequently, as shown in FIG. 6E, after deposition of reflecting layer606, a second phosphor layer application step is carried out to depositphosphor pixels 608. Phosphor pixels 608 are located where therectangular features in the checkerboard pattern of structure 502 (shownin FIG. 5) were previously located. The phosphor structures formed byfilling thin rectangular openings 506 in the previous phosphordeposition step prevent phosphor material deposited in the secondphosphor deposition step from flowing out of the array.

The phosphor material deposited in the second deposition step to formpixels 608 may be the same as that deposited in the first depositionstep to form pixels, 604. Alternatively, the phosphor materials used inthe two separate deposition steps may differ. For example, the phosphormaterials use in the two steps may comprise the same phosphors, andhence have the same or similar spectral characteristics, but differ inthe matrix material in which the phosphor particles are dispersed.Alternatively, the phosphor materials used in the two differentdeposition steps may use the same matrix material but comprise differentphosphors having different spectral characteristics. For example, in oneof the deposition steps a phosphor providing a warm white light outputmay be deposited while in the other phosphor deposition step a phosphorproviding a cool white light output may be deposited. This would resultin a matrix with about half warm white pixels and about half cool whitepixels, which might be advantageously employed in a camera flashapplication for example. The phosphor materials used in the two separatedeposition steps may also differ in both matrix and phosphor. After thesecond phosphor deposition step, the portion of the reflective layers ontop of phosphor pixels 604 are removed by chemical or mechanical means,for example, resulting in the phosphor pixel array shown in FIG. 6F.

As shown in FIG. 6G, the phosphor pixel array shown in FIG. 6F may beinverted and bonded to an array of LEDs 610 arranged on a substrate 612,with the phosphor pixels aligned with corresponding LEDs. This resultsin the structure shown in FIG. 6H.

Subsequently, carrier 602 and portions of reflective layer 606 presenton carrier 602 are removed by polishing or grinding (lapping). Thisresults in the pcLED array shown in FIG. 6I, in which adjacent closelyspaced phosphor pixels 614 are separated by reflective side walls 616.

Referring now to the partial cross-sectional views shown in FIGS. 7A-7D,in another variation of the phosphor deposition method an optionallyreusable mold 702 having openings as shown in FIG. 5, for example, isused instead of a photoresist pattern. Openings in the mold are filledwith a phosphor material to form phosphor pixels 704, and excessphosphor is removed from the top surface of the mold (FIG. 7A).

The mold may be formed from boron-nitride, for example, and may be usedfor example in combination with phosphor materials that cure at a highertemperature than photoresists can withstand. The phosphor material maybe, for example, a phosphor in glass (PiG) material. Any other suitablephosphor materials may be used instead. For example, the phosphormaterial may comprise a silicone or sol-gel matrix as described above,rather than a glass matrix.

Subsequently, phosphor pixels 704 are cured. For a PiG material,phosphor pixels 704 may be cured at about 480° C., for example. Thephosphor material may but will not necessarily shrink during curing, asdepicted in FIG. 7B. This might be compensated for by over-filling themold (see for example FIG. 8A discussed below).

Subsequently, the mold is inverted on a carrier 706 (FIG. 7C), and themold is removed after a further heating step that softens the phosphormaterial to attach and leave phosphor pixels 704 on the substrate aftercooling and removal of the mold. The carrier may be a glass sheet, forexample, or any other suitable material. If the phosphor material hasshrunk as depicted in FIG. 7B-7C, it might be difficult to get it torelease from the mold.

Alternatively, the phosphor material, a PiG material for example, isdeposited in the voids of the mold. Before curing the phosphor material,the substrate 706 is attached to the mold and the mold and substrateassembly is flipped to a configuration as shown in FIG. 7C followed by ahigh temperature curing step. The high temperature curing step, carriedout at about 480° C. for example, may be done under reduced pressure toimprove the density of the phosphor pixels 704 and the adhesion to thesubstrate 706.

Subsequent steps in forming the pcLED array in this variation of themethod may generally track those described with respect to FIGS. 6D-6I.

Referring now to the partial cross-sectional views shown in FIG. 8A-8B,another variation of the phosphor deposition method uses an optionallyreusable mold 702 as shown in FIG. 7A but overfills the mold withphosphor material 803 (FIG. 8A). As shown, in FIG. 8B, after removalfrom the mold this results in a monolithic phosphor structure comprisingphosphor pixels 804 connected to each other by a phosphor materialcarrier 806. Carrier 806 plays a role similar to carrier 706 shown inFIG. 7C. Subsequent steps in forming the pcLED array in this variationof the method may generally track those described with respect to FIGS.6D-6I.

In another variation of the phosphor deposition method, a checkerboardpattern as shown in FIG. 5 is formed by depositing a boron nitride gridon substrate 706. Such a boron nitride grid might be prepared bymicromachining, for example. Alternatively, a frame formed from boronnitride, for example, may be attached to or brought in contact with thesubstrate 706.

The frame or grid may be filled with phosphor material such as a PiGmaterial followed by a high temperature curing step that leads to aphosphor pixel on substrate configuration as shown in FIG. 7D, afterremoval of the frame or grid. For the filling process a PiG material canbe mixed with a liquid binder to obtain a paste or slurry. The paste orslurry can then be dosed into the openings of the frame or grid bymethods such as casting or dispensing, for example, followed by steps ofdrying and removal of the binder additives. Subsequent steps in formingthe pcLED array by these variations of the method may generally trackthose described with respect to FIGS. 6D-6I, with the boron nitride gridsubstituted for the photoresist pattern.

In variations in which a PiG material is deposited in a mold or frame,the mold or frame may be removed after glass melting and solidificationat a temperature chosen to maintain the pixel shape while avoidingmechanical stress resulting from mismatches between the coefficients ofthermal expansion of the mold or frame and the substrate, for example atthe glass softening or annealing temperature.

Referring now to the partial cross-sectional view of FIG. 9A, in anothervariation of the phosphor deposition method the phosphor material isdeposited directly on an LED array 900. LED array 900 comprises LEDs 100arranged on a substrate 902 in a rectangular array. Substrate 902 maycomprise CMOS configured to drive the LEDs via interconnects andcontacts 903.

As shown in FIG. 9B, a checkerboard photoresist pattern 502 is depositedon LED array 900, overlying alternate LEDs. A passivating dielectriclayer may be deposited on the LED array before deposition of thephotoresist.

Subsequently, as shown in FIG. 9C a phosphor material 905 is depositedin the checkerboard photoresist pattern. Excess phosphor is removed fromthe top of the LED array, leaving phosphor pixels 604 in place overcorresponding LEDs (FIG. 9D). The photoresist pattern may then beremoved, similarly to as described for other variations of the method,resulting in the structure shown in FIG. 9E.

Subsequent steps in forming the pcLED array in this variation of themethod may generally track those described with respect to FIGS. 6D-6I.

In variations of the phosphor deposition method employing a photoresistpattern 502 in combination with a phosphor material comprising phosphorparticles dispersed in a silicone matrix, it is desirable to cure thesilicone matrix at a temperature that satisfactorily cures the siliconebut is sufficiently low to avoid baking or damaging the photoresist andmaking the photoresist difficult to remove.

Such low temperature curing may be facilitated, for example, by using acondensation cure silicone composition for the matrix, and curing itusing vapor phase catalyzation. The condensation cure siliconecomposition may comprise organosiloxane block copolymers, for example.The vapor phase catalyst may be for example a basic or alkalinecatalyzing agent. Superbase catalysts such as described in U.S. Pat. No.9,688,035 by Swier et. al. can be used.

The term “superbase” used herein refers to compounds having a very highbasicity, such as lithium diisopropylamide. The term “superbase” alsoencompasses bases resulting from a mixing of two (or more) bases leadingto new basic species possessing inherent new properties. The term“superbase” does not necessarily mean a base that is thermodynamicallyand/or kinetically stronger than another. Instead, in some variations itmeans that a basic reagent is created by combining the characteristicsof several different bases. The term “superbase” also encompasses anyspecies with a higher absolute proton affinity (APA=245.3 kcal/mole) andintrinsic gas phase basicity (GB=239 kcal/mole) relative to1,8-bis-(dimethylamino)-naphthalene. Non-limiting examples of superbasesinclude organic superbases, organometallic superbases, and inorganicsuperbases.

Organic superbases include but are not limited to nitrogen-containingcompounds. In some embodiments, the nitrogen-containing compounds alsohave low nucleophilicity and relatively mild conditions of use.Non-limiting examples of nitrogen-containing compounds includephosphazenes, amidines, guanidines, and multicyclic polyamines. Organicsuperbases also include compounds where a reactive metal has beenexchanged for a hydrogen on a heteroatom, such as oxygen (unstabilizedalkoxides) or nitrogen (metal amides such as lithium diisopropylamide).In some embodiments, the superbase catalyst is an amidine compound. Insome embodiments, the term “superbase” refers to organic superbaseshaving at least two nitrogen atoms and a pKb of from about 0.5 to about11, as measured in water.

Organometallic superbases include, but are not limited to, organolithiumand organomagnesium (Grignard reagent) compounds. In some variations,the organometallic superbases are hindered to the extent necessary tomake them non-nucleophilic.

Superbases also include mixtures of organic, organometallic, and/orinorganic superbases. A non-limited example of such mixed superbases isthe Schlosser base (or Lochmann-Schlosser base), which is thecombination of n-butyllithium and potassium tert-butoxide. Thecombination of n-butyllithium and potassium tert-butoxide form a mixedaggregate of greater reactivity than either reagent alone and withdistinctly different properties in comparison to tert-butylpotassium.

Inorganic superbases include salt-like compounds with small, highlycharged anions. Non-limiting examples of inorganic superbases includelithium nitride and alkali- and alkali earth metal hydrides includingpotassium hydride and sodium hydride. Such species are insoluble in allsolvents owing to the strong cation-anion interactions, but the surfacesof these materials are highly reactive and slurries can be used.

In some variations the superbase catalyst comprises1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), (CAS #6674-22-2)

The amount of the superbase catalyst used can vary and is not limiting.Typically, the amount added through vapor phase is a catalyticallyeffective amount, which may vary depending on the superbase selected,and vapor permeation properties of the siloxane polymer resin. Theamount of superbase catalyst is typically measured in parts per million(ppm) in the solid composition. In particular, the catalyst level iscalculated in regard to copolymer solids. The amount of superbasecatalyst added to the curable silicone compositions may range from 0.1to 1,000 ppm, alternatively from 1 to 500 ppm, or alternatively from 10to 100 ppm, as based on the polymer resin content (by weight) present inthe solid compositions.

The silicone material or siloxanes can be selected for mechanicalstability, low temperature cure properties (e.g. below 150-120 degreesCelsius), and ability to be catalyzed using vapor phase catalysts. Insome variations, organosiloxane block copolymers can be used.Organopolysiloxanes containing D and T units, where the D unit areprimarily bonded together to form linear blocks having 10 to 400 D unitsand the T units are primarily bonded to each other to form branchedpolymeric chains, which are referred to as “non-linear blocks” can beused.

This disclosure is illustrative and not limiting. Further modificationswill be apparent to one skilled in the art in light of this disclosureand are intended to fall within the scope of the appended claims.

1-12. (canceled)
 13. A matrix array of phosphor pixels comprising: acarrier; a plurality of first phosphor pixels positioned on the carrierto form a first checkerboard pattern in which first phosphor pixels arepositioned in alternating locations in the matrix array alternating withlocations in which first phosphor pixels are not positioned, each of thefirst phosphor pixels comprising a top surface, a bottom surfaceopposite the top surface, and sidewalls connecting the top surface andthe bottom surface; a plurality of second phosphor pixels positioned onthe carrier to form a second checkerboard pattern in which the secondphosphor pixels are positioned in alternating locations in the matrixarray alternating with locations in in which the first phosphor pixelsare positioned, each of the second phosphor pixels comprising a topsurface, a bottom surface opposite the top surface, and sidewallsconnecting the top surface and the bottom surface; a plurality ofreflective structures disposed between sidewalls of the first phosphorpixels and the second phosphor pixels adjacent to each other, anddisposed between second phosphor pixels and the carrier.
 14. The matrixarray of claim 13, wherein the reflective structures comprise sidewallsthat are disposed between sidewalls of the first phosphor pixels and thesecond phosphor pixels adjacent to each other, and a bottom surfaceconnecting the sidewalls.
 15. The matrix array of claim 14, wherein thebottom surface of the reflective structures is in direct contact withthe carrier.
 16. The matrix array of claim 14, wherein the bottomsurface of the reflective structures is in direct contact with thesecond phosphor pixels.
 17. The matrix array of claim 13, wherein thereflective structures are not positioned between the first phosphorpixels and the carrier.
 18. The matrix array of claim 17, wherein thefirst phosphor pixels are in direct contact with the carrier.
 19. Thematrix array of claim 13, wherein the first phosphor pixels havesidewalls with greater heights than heights of sidewalls of the secondphosphor pixels.
 20. The matrix array of claim 13, wherein a planarshape of the top surface of the first phosphor pixels is a square shapeand a planar shape of the top surface of second phosphor pixels is asquare shape.
 21. The matrix array of claim 13, wherein the matrix arrayfurther comprises thin rectangular phosphor walls disposed at the outeredges of the matrix array to surround the first checkerboard pattern andthe second checkerboard pattern, each of the thin rectangular phosphorwalls having a top surface having a non-square planar shape.
 22. Thematrix array of claim 21, wherein a length of the top surface of thethin rectangular phosphor walls is a same length as a length of the topsurface of the first phosphor pixels or of the second phosphor pixels,and a width of the top surface of the thin rectangular phosphor walls isa different width than a width of the top surface of the first phosphorpixels or of the second phosphor pixels.
 23. The matrix array of claim13, wherein the first phosphor pixels and the second phosphor pixelsadjacent to each other are spaced apart by less than or equal to about10 microns by the reflective structures.
 24. The matrix array of claim23, wherein the first phosphor pixels and the second phosphor pixelsadjacent to each other are spaced apart by less than or equal to about 3microns by the reflective structures.
 25. The matrix array of claim 13,wherein the reflective structures comprise at least one of aluminum,silver, and a multilayer Distributed Bragg Reflector structure.
 26. Thematrix array of claim 13, wherein the first phosphor pixels and thesecond phosphor pixels comprise at least one of silicone, sol gel, andglass.
 27. The matrix array of claim 13, wherein at least one of thefirst phosphor pixels and the second phosphor pixels comprisesorganosiloxane block copolymers.
 28. The matrix array of claim 13,wherein the first phosphor pixels comprise first phosphors withdifferent spectral characteristics than second phosphors comprised inthe second phosphor pixels.
 29. The matrix array of claim 13, whereinthe first phosphors pixels comprise first phosphors with same spectralcharacteristics as second phosphors comprised in the second phosphorpixels, and the first phosphor pixels comprise a first matrix materialin which the first phosphors are dispersed that is a different matrixmaterial than the second matrix material comprised in the secondphosphor pixels in which the second phosphors are dispersed.
 30. Thematrix array of claim 13, wherein the carrier is glass.
 31. A method offabricating a matrix array of phosphor-converted LEDs, the methodcomprising: depositing first phosphor material in openings in a mold;curing the first phosphor material deposited in the openings in themold; inverting the mold to deposit the first phosphor material atalternating locations in a matrix array to form a checkerboard patternof first phosphor pixels in which locations in the matrix array at whichfirst phosphor pixels are deposited alternate with locations in thearray at which first phosphor pixels are not deposited, the firstphosphor pixels comprising side walls adjacent to and facing thelocations in the array at which the first phosphor pixels are notdeposited; depositing reflective structures on the side walls of thefirst phosphor pixels; and after depositing the reflective structures,depositing a second phosphor material to form second phosphor pixels atthe alternating locations in the matrix array at which the firstphosphor pixels are not deposited, such that the first phosphor pixelsadjacent to the second phosphor pixels in the resulting matrix array arein contact with and spaced apart by the reflective structures.
 32. Amethod of fabricating a matrix array of phosphor-converted LEDs, themethod comprising: depositing a first phosphor material in openings in amold to overfill the openings; curing the first phosphor materialdeposited in the openings in the mold to overfill the openings;inverting the mold, then removing the mold to provide a monolithicphosphor structure comprising first phosphor pixels at alternatinglocations in a matrix array forming a checkerboard pattern so thatlocations in the matrix array at which phosphor pixels are depositedalternate with locations in the array at which phosphor pixels are notdeposited, the first phosphor pixels comprising side walls adjacent toand facing the locations in the array at which phosphor pixels are notdeposited, the first phosphor pixels connected to each other by aphosphor material carrier; depositing reflective structures on the sidewalls of the first phosphor pixels; and after depositing the reflectivestructures, depositing a second phosphor material to form secondphosphor pixels at the alternating locations in the matrix array atwhich the first phosphor pixels are not deposited, such that the firstphosphor pixels adjacent to the second phosphor pixels in the resultingmatrix array are in contact with and spaced apart by the reflectivestructures.